Species' gender

George, surely there is much diversity between types of bacteria... but little between generations (if we can even call them that) of the same line of bacteria.The strength of sexual reproduction is that it produces a range of (subtlely (sp?)) different offspring rather than clones- you get differences due to jumbling of genes as well as simply mutations.For an organism well adapted to its niche this is no real advantage, since if one is well adapted all will be, but if circumstances change then a species with the ability to vary between generations suddenly benefit since even if the parents can't cope some of the offspring will and can repopulate.Of course one of the big differences between bacteria and, say, mammals, is going to be that the generation time is much shorter... bacteria, if they're reproducing every couple of hours, will get through a lot of generations (ergo a lot of opportunities for favourable or less favourable mutations in the line) in a given time (say a year or two, or a number of decades) whereas the best mammals can manage is one generation every month or two (many of course much less) so a change in the environment over a period of a few years will leave more species high and dry unless they can shortcut the mutation and use sexual reproduction instead (well, OK, as well...).

Obviously sexual reproduction only works where there is at least one compatible sexual partner available... so there's an element of returning to the norm over time unless there's a strong selection for a particular characteristic... but if there's a strong evolutionary pressure that selects for (say) individuals that have huge (secondary sexual) antlers then the species will drift toward having huge antlers (even if it causes the species to become entirely non-viable and die out... I think there was a species of Irish moose-type-animal that suffered this fate, can't remember the details).